Self-orienting radio direction finder



March 16, 1943. D. s. BOND ET AL SELF-ORIENTING RAD IO DIRECTION FINDER Filed March 19, 1938 2 Sheets-Sheet 1 u k 0 oamofl f WE /r 3nnntor5 DON/7A0 5. 50/1 0 m z 4. 648150 (Itto rneg March 16, 1943. BOND ETAL 2,314,029

SELF-ORIENTING RADIO DIRECTION FINDER Filed March 19, 1938 2 Sheets-Sheet 2 n A/aa z Gttorneg Patented Mar. 16, 1943 SELF- ll-pr.

'l' G RADIO DIRECTION ware Application March 19, 1938, Serial No. 196,817

15 Claims.

Our invention relates to self-orienting radio direction finders, and particularly to a self-orienting direction finder in which the torque of the motor orienting the directive antenna is increased in the region adjacent the null point.

It has been proposed to couple a directive antenna to a motor whereby the directive antenna may be rotated until zero signal is induced in the antenna. At this position relay contacts or the like disengage the motor. Such systems are not entirely satisfactory because relay contacts are not always certain of operation. We propose to use a two-phase motor and adjust its movements by applying a current of fixed phase to one of the field windings of the motor and a current of reversible phase, which depends upon the orientation of the directive antenna, to the other field winding. When thus arranged, the twophase motor will drive the directive antenna. until a point of minimum or zero signal is reached. At this point, only the reference phase current is applied to the rotor, hence no rotation of the rotor takes place. We have found that a low motor torque, in the region near the point of null signal in the directive antenna, makes it difiicult to operate a self-orienting antenna by means of an ordinary arrangement of radio receiver and two-phase motor.

One of the objects of our invention is to provide means for operating a self-orienting directive antenna by means of a two-phase motor. Another object is to provide means in a selforienting direction finder whereby the motor torque is increased in the region near the minimum signal response. A further object is to provide means in a self-orienting direction finder whereby automatic sensitivity control is used to maintain the receiver output substantially constant.

In describing the invention, reference will be made to- Figure 1, which is a circuit diagram illustrating one embodiment of our invention;

Figures 2 and 3 are response curves which illustrate the theory of operation; and

Figure 4 is a block diagram illustrating a modification of the invention.

Referring to Fig. 1, a shielded rotatable loop or any rotatable directive antenna is connected to the input of a radio frequency amplifier 3 by means of a radio frequency transformer 5. The output circuit 6 of the radio frequency amplifier includes elements which are adjusted to offer either an inductive or a capacitive reactance which advances or retards the phase of the currents substantially The output 6 of the radio frequency amplifier is connected to a pair of balanced modulators I, 9. The output circuit of the balanced modulators is coupled by a primary winding II to a radio frequency transformer I3. Antenna I5 is also coupled by a primary winding H to the secondary of the radio frequency transformer. The secondary of the radio frequency transformer is connected to a radio receiving device IS. The radio receiving device may include a radio frequency amplifier, a detector, a local oscillator, an intermediate frequency amplifier, a second detector, an automatic sensitivity control, and an output circuit, which may include an audio frequency amplifier.

The output of the audio amplifier is connected to a thermionic amplifier 2|. The output circuit of the thermionic amplifier is connected to a band pass filter 23 which, in turn, is connected to an audio amplifier tube 25. The output of the audio amplifier is applied to a pair of tubes 21, 29 which are connected in push-pull relation to an audio frequency transformer 3|. The secondary of the audio frequency transformer. is connected to one field winding 33 of a two-phase motor 35. The other field winding 31 of the motor is connected through a phase shifter 39 to an alternating current source which may be a generator 4| or the like. The generator is connected to a transformer. The secondary 45 of this transformer is connected in push-pul1 relation to the balanced modulator tubes 1, 9 by series impedances 46.

A connection 41 is made from the audio amplifier circuit 25 to the anode 49 of a diode rectifier which may be a part of the radio frequency amplifier 3 or a separate rectifier. The anode is also connected'to ground by resistors 5|. A connection is made from a point intermediate the ends of the resistors 5|, through a filter 53, to the lower end of the secondary of the radio frequency transformer 5, which is connected to'the control grid of the radio frequency amplifier 3. This connection may include a source 56 of grid bias voltage, which may be derived from any suitable source to thereby make the control grid bias independent of the self-bias. The cathode of the diode may be grounded through a self-bias resistor 56, which provides a delay voltage. The term delay voltagerefers to the threshold value of voltage at which the audio automatic, sensitivity control operates rather than the time" at which it operates.

The operation of the foregoing circuit is essentially as follows: Signal currentawhich are induced in the loop and amplified by the radio frequency amplifier 3, are applied to the balanced modulators I, 9 which are alternately keyed by potentials from the audio frequency generator 4|. There are thus provided in the output circuit of the balanced modulator, modulated currents of side band frequency with a suppresesd carrier frequency current. Because of the 90 phase shift in the radio frequency ampiifier output circuit, the currents of side band frequency may be combined with carrier frequency currents from the non-directive antenna It so that the figure 8 response pattern of the loop, combined with the circular response pattern of the non-directive antenna, becomes a cardioid pattern. The output of the radio receiving device 19 will include currents of modulation frequency. The amplitude of these currents will vary and their phase reverse as a function of the loop orientation with respect to the wave front passing through the loop. These audio frequency currents of variable amplitude and reversible phase are applied to one of the field windings 33 of the two-phase motor. Currents of the same frequency but of fixed phase relation are applied to the other field winding 31. Therefore, depending upon the phase of I the current derived from thereceived signals,

the rotor 55 will be moved either clockwise or counter-clockwise. If no modulation currents are derived, 1. e., when the loop is in the null position, no rotor movement will take place because only the reference phase current will be applied. Since the rotor is coupled to the loop by suitable means, indicated by the reference number 51, the loop will be rotated until a null position is reached. The loop position may be indicated by a pointer 58 and associated scale 80.

Neglecting for the moment the efiect of audio frequency control ofthe sensitivity of the radio frequency amplifier 3, we have found that the ratio of the loop signal to the non-directional antenna signal is too small when the loop position approaches its null point, or too large when the loop is remote from its null position. The former condition may cause under-modulation and the latter over-modulation of the carrier current derived from the non-directive antenna. If the side band voltages in the output of the balanced modulator tubes greatly exceed the voltage from the non-directional antenna, the carrier from the antenna will be greatly over-modulated. Over-modulation reduces the fundamental components of the audio output. If the carrier is thus either under or over-modulated, the audio frequency output becomes greatly diminished and, since one of the phases of the audio frequency which operate the motor is thus diminished, the motor torque becomes very low. This condition is illustrated in Fig. 2.

To prevent the modulation components in the' balanced modulators 1, 9 from over-modulating the carrier frequency currents in the non-directive antenna l5, we have arranged the automatic sensitivity control which operates as a function of the audio frequency output and thus can be designed to automatically increase or diminish the sensitivity of the radio frequency amplifier 3 to thereby maintain a substantially constant percentage modulation or constant audio frequency output. In this manner, over-modulation or under-modulation of the carrier frequency is prevented and thereby the audio frequency output currents of the receiving device I! are maintained substantially constant so that the motor torque is substantially maintained until the null position is almost reached, as illuscurrents to derive output currents whose phases reverse as a function of loop orientation. In order that the modulated loop currents will not over-modulate or under-modulate the carrier frequency current to thereby diminish the audio frequency output, an automatic sensitivity control is coupled to the audio output circuit of the receiver to thereby control the sensitivity of the loop amplifier as a function of the audio frequency output, The operation of the automatic sensitivity control derived from the audio voltage may be delayed to thereby control the shape of the control curve. It should, be understood that the same invention may be used on a leftright indicator which may be substituted for the two-phase motor which orients the loop.

Likewise, the audio derived automatic sensia tivity control voltage may be applied to change the carrier voltage (derived from the non-di rective antenna) so that the percentage modulation may be maintained substantially constant. If applied to regulate the carrier voltage from the non-directive antenna, we prefer to use an additional radio frequency amplifier which will be controlled inversely as the control applied to the amplifier preceding the balanced modulator. I

Such an arrangement is schematically illustrated in Fig. 4. The directive antenna ill is connected through a radio frequency amplifier I03 to a balanced modulator I05. The balanced modulator is connected to an audio frequency generator III, which is also connected through a phase shifter I09 to a reversible motor Ill. The output of the balanced modulator I35 is applied to a radio receiver 3 which includes a demodulator. The radio receiver 3 has an input circuit which is connected through a radio frequency amplifier and phasing circuit III to'a non-directive antenna 1. The radio receiver output is applied to an audio amplifier H0 and hence to a band pass filter III. The output from the band pass filter is impressed on a second audio amplifier I23 and hence upon the reversible motor. III to apply thereto the current of second phase. The motor III is coupled mechanically to the directional antenna ill and to an indicator I25. The output of the band pass filter m is also impressed on an automatic sen- I the elements which make up the circuit because the several elements previously described may be substituted for the corresponding elements of the block diagram.

We claim as our invention:

1. In a radio direction finder, the combination of a directive antenna, a non-directive antenna, an amplifier connected to said directive antenna, said amplifier including means for shifting the phase of the, amplified currents in a constant direction independently of their frequency, a modulation current source, a balanced modulator connected to said source and supplied with high frequency currents derived from said directive antenna for modulating said last mentioned derived currents to produce currents of side band frequency, a radio receiver, means for applying a carrier frequency current derived from said non-directive antenna and currents of side hand frequency derived from said directive antenna to said receiver so that a demodulated current corresponding to said side band frequency may be derived from said receiver, means for rectifying said demodulated current to derive a controllng voltage, and means for applying said controlling voltage to said amplifier.

2. A radio direction finder including, in combination, a directive antenna, a non-directive antenna, radio frequency amplifier connected to said directive antenna, said amplifier including means for shifting the phase of the amplified rective antenna and said balanced modulator to said radio receiver, means for deriving an audio frequency output current from said receiver, said audio current varying in amplitude and reversing in phase as a function of the angular relation between said directive antenna and an approaching wave front, means for deriving a controlling voltage from said audio output current, and means for applying said controlling voltage to said radio frequency amplifier to maintain said audio frequency current substantially constant in amplitude for a signal received throughout the regions of the directive response of said directive antenna excepting the positions adjacent the null points of said directive antenna.

3. A radio direction finder including, in comblnation, a directive antemia, a non-directive antenna, a radio frequency amplifier connected to said directive antenna, said amplifier including means for shifting the phase of the amplified currents in a constant direction independently of their frequency, a radio receiver, a balanced mod- I ulator connected to said radio frequency amplifier and supplied with in phase radio frequency currents derived from said directive antenna, an audio frequency current source, means for applying currents from said source in out of phase relationship to said balanced modulator to modulate said radio frequency currents, means coupling said non-directive antenna and said balanced modulator to said radio receiver, means for deriving an audio frequency current from said receiver, said audio current varying in amplitude and reversing in phase as a function of the position of said directive antenna, means for deriving a. controlling voltage from said audio frequency current, and means for applying said controlling voltage to said radio frequency amplifier to thereby maintain said audio frequency current substantially constant in amplitude for a signal received in all positions of said directive antenna excepting the positions adjacent the null points of said directive antenna.

4. A radio direction finder including, in combination, a directive antenna, a non-directive antenna, a radio frequency amplifier connected to said directive antenna, said amplifier including means for shifting the phase of the amplified currents in a constant direction independently of their frequency, a radio receiver, a balanced modulator connected to said radio frequency amplifier, means forjapplying an audio frequency modulation current to said balanced modulator, means coupling said non-directive antenna and said balanced modulator to said radio receiver, means for deriving an audio frequency current from said receiver, said audio current varying in amplitude and reversing in phase as a function of the position of said directive antenna, means for deriving a controlling voltage from said audio output current, and means for applying said controlling voltage to said radio frequency amplifierso that said audio frequency current is maintained substantially constant for a signal received in all positions of said directive antenna excepting the positions adjacent the null points of said directive antenna.

5. A radio direction finder including, in combination, a directive antenna, a non-directive antenna, a radio frequency amplifier connected to said directive antenna, said amplifier including means for shifting the phase of the amplified currents in a constant direction independently of their frequency, a radio receiver, a balanced modulator connected to said radio frequency amplifier, means for applying an audio frequency modulation current to said balanced modulator,

means coupling said non-directive antenna and said balanced modulator to said radio receiver, means'for deriving an audio frequency current from said receiver, said audio current varying in amplitude and reversing in phase as a. function of the position of said directive antenna, means for deriving a controlling voltage from said audio output current, means for applying said controlling voltage to said radio frequency amplifier so that said audio frequency current is maintained substantially constant for a signal received in all positions of said directive antenna excepting the positions adjacent the null points of said directive antenna, a reversible motor, means coupling said motor to said directive antenna, and means for applying said audio frequency modulation current and said derived audio frequency current to said control motor so that it is operated to orient said directive antenna as a function of said substantially constant audio frequency current.

6. A radio direction finder including, in combination, a directive antenna, a non-directive antenna, a radio frequency amplifier connected to said directive antenna, said amplifier including means for shifting the phase of the amplified currents in a constant direction independently of their frequency, a radio receiver, a balanced modulator connected to said radio frequency amplifier and supplied with high frequency currents derived from said direction; antenna, a source of audio modulation current, means for applying said modulation current to said balanced modulator for modulating current derived from said directive antenna for producing current of sideband frequency, means coupling said nondirective antenna and said balanced modulator to said radio receiver, means for deriving an audio frequency output current from said receiver, said audio current varying in amplitude and reversing in phase as a function of the angular relation between said directive antenna. and an approaching wave front, means for deriving a controlling voltage from said audio output current, means for applying said controlling voltage to said radio frequency amplifier to maintain said audio frequency current substantially constant in amplitude for a signal received throughout the regions of the directive response of said directive antenna excepting the positions adjacent the null points of said directive antenna, a reversible motor, means mechanically coupling said motor to said directive antenna, and means for applying said audio frequency current to said motor to control its operation and to orient said directive antenna as a function of the signals received thereon.

7. A radio direction finder including, in combination, a directive antenna. a non-directive antenna, a radio frequency amplifier connected to said directive antenna, said amplifier including means for shifting the phase of the amplified currents in a constant direction independently of their frequency, a radio receiver, a balanced modulator connected to said radio frequency amplifier and supplied with high frequency currents derived from said direction antenna, a source of audio modulation current, means for applying said modulation current to said balanced modulator for modulating current derived from said directive antenna for producing current of sideband frequency, means coupling said nondirective antenna and said balanced modulator to said radio receiver, means for deriving an audio frequency output current from said receiver, said audio current varying in amplitude and reversing in phase as a function of the angular relation between said directive antenna and an approaching wave front, means for deriving a controlling voltage from said audio output current, means for appLving said controlling voltage to said radio frequency amplifier to maintain said audio frequency current substantially constant in amplitude for a signalreceived throughout the regions of the directive response of said directive antenna excepting the positions adjacent the null points of said directive antenna, a two-phase motor including field windings, a source of modulation frequency current, means for applying said modulation frequency current to said balanced modulator and to one of the field windings of said motor, and means for applying to the other of said field windings said derived audio frequency current, and means coupling said motor to said directive antenna so that said directive antenna is oriented as a function of said modulation frequency currents and said substantially constant audio frequency current.

8. In a direction finder including a motor for orienting a directional antenna, the method of indicating direction which comprises deriving a first carrier frequency current from waves whose wave fronts are to beindicated, deriving a second carrier current which varies in amplitude as a function of the disposition of said wave front, modulating said second carrier current, deriving currents of side band frequency and eliminating the carrier frequency of said modulator carrier, combining said first carrier and said side band frequency currents, demodulating said currents, deriving a controlling voltage from said demodulated currents, applying said controlling voltage to one of said carrier currents to maintain the amplitude of said demodulated currents substantially constant except when said second carrier currents are at their null condition, and indicating direction by applying said modulating currents and said demodulated currents to said motor to orient said directional I current which varies in amplitude and reverses in phase as a function of said angular relationship, applying modulation currents to said second carrier current, deriving side band frequency currents from said modulated carrier, eliminating currents of said second carrier frequency, combining said first carrier and said side band frequency currents, demodulating said combined currents, deriving a controlling voltage from said demodulated currents, applying said controlling voltage to one of said carrier currents to maintain substantially constant percentage of said side band currents with respect to said first carrier currents except in the region where said phase reverses, deriving forces from said modulation currents, deriving forces from said demodulation currents, and applying said forces to operate said motor to orient said directive antenna and said indicator.

10. In a direction finder including a directive and a non-directive antenna, and a motor for orienting said directive antenna, the method of orienting an indicator to indicate the angular relation of auwave front and said directive antenna which comprises deriving a carrier frequency current from said non-directive antenna,

, deriving a second carrier frequency current which varies in amplitude and reverses in phase as a function of said angular relationship, applying modulation currents to said second carrier current, deriving side band frequency currents from said modulated carrier, eliminating currents of said second carrier frequency, combining said first carrier and'said side band frequency currents, demodulating said combined currents, deriving a controlling voltage from said demodulated currents, applying said controlling voltage to one of said carrier currents to maintain substantially constant percentage of said side band currents with respect to said first carrier currents except in the region where said phase reverses, deriving forces from said modulation currents, deriving forces from said demodulation currents, and applying said forces to said motor to orient said directive antenna so that it indicates its relation to said wave front.

11. In a direction finder including a directive and a non-directive antenna and an orienting motor, the method of orienting said directive antenna to indicate the angular relation of a wave front and said directive antenna which comprises deriving a carrier frequency current from said non-directive antenna, deriving a second carrier frequency current which varies in amplitude and reverses in phase as a function of said angular relationship, amplifying said second carrier current, applying modulation currents to said amplified second carrier current, deriving side band frequency currents from said modulated carrier, eliminating currents of said second carrier frequency, combining said first carrier and said side band frequency currents, demodulating said combined currents, deriving a controlling voltage from said demodulated currents.

applying said controlling voltage to control said amplifying and to thereby maintain substantially constant percentage of said side band currents with respect to said first carrier currents except in the region where said phase reverses, applying said modulation currents and said demodulated currents to said motor to control the orientation of said directive antenna as a function of the angular relation between said directive antenna and said wave front.

12. A radio direction finder including, in combination, a directive antenna, a non-directive antenna, a radio frequency amplifier connected to one of said antennas, said amplifier including a phase changing circuit, a radio receiver, a balanced modulator effectively connected to the other of said antennas and supplied with currents from said antenna, a source of audio current, means for applying said audio current to said balanced modulator to modulate said antenna currents, means coupling the output of said radio frequency amplifier and said balanced modulator to said radio receiver, means for deriving an audio frequency current from said receiver, said audio current varying in amplitude and reversing in phase as a function of the position of said directive antenna, means for deriving a controlling voltage from said audio frequency current, and means for applying said controlling voltage to said radio frequency amplifier to thereby maintain said audio frequency current substantially constant in all positions of said directive antenna excepting the positions adjacent the null points of said directive antenna.

13. A radio direction finder including, in combination, a directive antenna, a non-directive, antenna, a radio frequency amplifier connected to said directive antenna, said amplifier including a phase changing circuit, a radio receiver, a balanced modulator connected to said radio frequency amplifier and supplied with high frequency currents from said directive antenna, a source of audio current, means for applying said audio current to said balanced modulator to modulate said antenna currents, means coupling said non-directive antenna and said balanced modulator to said radio receiver, means for deriving an audio frequency current from said receiver, said audio current varying in amplitude and reversing in phase as a function of the position of said directive antenna, means for deriving a controlling voltage from said audio frequency current, and means for applying said controlling voltage to said radio frequency amplifier to thereby maintain said audio frequency current substantially constant in all positions of said directive antenna excepting the positions adjacent the null points of said directive antenna.

14. A radio direction finder including, in combination, a directive antenna, a non-directive antenna, a radio frequency amplifier connected to said non-directive antenna, said amplifier including a phase changing circuit, a balanced modulator connected to said directive antenna and supplied in phase high frequency currents therefrom, a source of audio frequency current, means for applying said audio frequency current in out of phase relation to said balanced modulator, means coupling the output of said amplifier and said balanced modulator to said radio receiver, means for deriving an audio frequency current from said receiver, said audio current varying in amplitude and reversingin phase as a function of the position of said directive antenna, means for deriving a controlling voltage from said audio frequency current, and means for applying said controlling voltage to said radio frequency amplifier to thereby maintain said audio frequency current substantially constant in all positions of said directive antenna excepting the positions adjacent the null points of said directive antenna.

15. A radio direction finder including, in combination, a directive antenna, a non-directive antenna, a. radio frequency amplifier connected to one of said antennas and including a phase changing circuit, a second radio frequency amplifier connected to the other of said antennas, a radio receiver, a balanced modulator connected to the output of one of said radio frequency amplifiers, means coupling the output of the radio frequency amplifier which is not coupled to the balanced modulator and the output of said balanced modulator to said radio receiver, means for deriving an audio frequency current from said receiver, said audio frequency current varying in amplitude and reversing in phase as a function of the position of said directive antenna, means for deriving a controlling voltage from said audio frequency current, and means for applying said controlling voltage to either of said radio frequency amplifiers to thereby maintain said audio frequency current substantially constant in all but the null positions of said directive antenna.

DONALD S. BOND. WENDELL L. CARLSON. 

